The reason is that thing called tax incidence. Companies don't pay corporation tax: it's some combination of the shareholders and the workers who do. This is not a point in argument: the only argument is about what the portions are, not the fact that the burden falls upon these two groups. We also know what it is that influences which group: it's how large the economy is in relation to the world economy and how open it is to capital movement. The smaller and more mobile, the more the workers get it in the neck.

The mechanism is simple enough. It's pretty much straight from Adam Smith in fact. There's an average rate of return to capital: a jurisdiction that taxes that return to capital will have a return lower than that global average. So, some domestic capital will flow out seeking the higher foreign returns, some foreign capital will not flow in for the lower domestic ones. There's thus less capital employed in the economy. Adding capital to labour is what drives up the productivity of labour: the average wages in a country are determined by the average productivity in that economy. So, tax companies, get less capital employed, wages are lower than they otherwise would be. The workers are bearing part of the burden.

As I say, the smaller the economy and the more open it is then the more of that burden is upon the workers. And in a wonderful result back in 1980 Joe Stiglitz showed that the burden upon the workers can actually be more than 100%. That is, the workers lose more in wages than the government gets in tax.